I worked in a critical access OB unit as a CNA. Generally the RN's do L&D and postpartum. We had about 30 births a month, usually 3 nurses per shift, one CNA per shift. There was quite a bit of low censusing there- I could count on getting put on call once every pay period.
OB nurses were floated as needed to the medical unit, generally given the most stable patients- no contact precautions patients just in case they had to go back down to the OB unit.
As far as support, eh... depends on your coworkers and their skill level. At the CAH I worked at, the hospital would pull together well when one unit was having an emergency. The house sup was the go to, a typically an experienced ICU nurse who would jump in and help out, especially with major traumas, codes, or emergency transports. Our hospital had an RT on staff 24/7 and laboratory services, but in some hospitals you might have to do those things yourself.